Prominent Conservative backbencher Adam Afriyie has said he will try to force the government to hold an early vote on whether the UK should leave the EU.

The prime minister has promised to hold an in/out referendum in 2017 if he wins the next general election, but Mr Afriyie said voters were "not convinced" that it would happen.

He said he would push for a vote in October 2014 instead.

But Home Secretary Theresa May warned that Mr Afriyie had "got it wrong".

And a Downing Street spokesman said of Mr Afriyie's plan: "The PM will not let it stand."

Mr Afriyie - who has denied newspaper claims he is being groomed to replace party leader David Cameron - said he would table an amendment to the European Union (Referendum) Bill on Monday.

'Absolutely delighted'

Mr Cameron has pledged to renegotiate the UK's relationship with the EU before an in/out referendum in 2017.

But, speaking on the BBC's Sunday Politics programme, Mr Afriyie said there would be "ample time" to conduct this renegotiation by as early as next year.

"By having a referendum in 2014, it gives us 12 months to renegotiate," he said. "But more than that, it kick-starts negotiations."

We will not allow this amendment to be passed under any circumstances - the PM will not let it standDowning Street spokesman

EU member states would need to "accommodate" British demands for reforms "if they wish us to remain", he added.

He argued: "I think it strengthens the prime minister's hand."

The MP said 80% of people wanted a referendum, and more than 50% of people wanted a referendum this side of the election.

"British businesses need certainty," he said, adding he had struggled with his conscience over the matter.

"I don't want to cause any trouble over it, but I think it's absolutely essential that Parliament and MPs have the opportunity to search their souls and to give people a referendum this side of the election."

In an article for the Mail on Sunday, he predicted that, without a referendum before 2015, "large numbers of people will continue to vote UKIP whatever happens, and if they do, there is a distinct danger that Labour will gain a majority and we will never see a referendum at all".

UKIP leader Nigel Farage said he would be "absolutely delighted" if the nation could have a referendum before 2015, adding it would benefit British business.

Media captionUKIP leader Nigel Farage says he would be "absolutely delighted" by a potential referendum over the EU

He told the BBC's Andrew Marr programme: "Adam Afriyie has put his finger on the real problem - and that's that four years ago, Mr Cameron gave us a cast-iron guarantee that there would be a referendum.

"This time last year, he was saying there would not be a referendum, and he is now saying there should be a referendum. People are not quite sure what to believe."

But Mrs May told the BBC: "We need to be negotiating that settlement with the European Union and then put to the British people the Europe of the future - not the Europe of the past - and give them that opportunity to say in or out.

"What is crucial is that we have, at the next election, a Conservative party that will be offering people that renegotiation of a new settlement with Europe, looking to the future and then putting that to the British people in an in/out referendum."

Backbench Conservative MP James Wharton is attempting to enshrine his party leadership's referendum pledge in law - without the support of coalition partners the Liberal Democrats - with his European Union (Referendum) Bill.

As a private member's bill, it is vulnerable to being delayed by procedural tactics from MPs who oppose it, and will only become law if the government allocates enough parliamentary time for its proponents to overcome any such hurdles.

Mrs May warned Mr Afriyie's amendment to the bill could "jeopardise" its prospects entirely.

"My concern is that any amendment, no matter how well-meaning it might be, is going to make the progress of the bill more difficult and it'll make it easier for those MPs who want to use procedural techniques to slow it down and stop it... that bit more possible.

"I don't want to see that. I'd like to see my bill go through and I think this harms the chances of that happening."

Liberal Democrat deputy leader Simon Hughes, whose party opposes a referendum on the EU unless further powers are handed from Westminster to Brussels, said a 2014 referendum would be a "barmy" distraction from attempts to boost UK economic growth.

Deputy Prime Minister and Lib Dem leader Nick Clegg said the Conservative leadership had scheduled a referendum in 2017 due to "internal party management as much as anything else".

The PM's promise of a "grand, unilateral renegotiation of Britain's relationship with the EU" was "deeply flawed and bound to unravel", he added, in pre-released extracts of a speech to be delivered in London on Tuesday.

Labour Party vice-chair, Michael Dugher MP, said "the Tories are back to obsessing about the European Union".

"We need a prime minister and a government that will make dealing with the cost of living the number one priority. Instead David Cameron is too weak and out of touch to stop this latest outbreak of Tory infighting."

The European Union (Referendum) Bill is due to return to the House of Commons for further debate on 8 November.